I need some help

Ok, I need to know a few things: 1.) I am making a game, and the characters can fly, I know that you can keep characters that walk in the level by unpassable terrain and such, but if this is outside, how do I convincably contain a flying character within the level. 2.) How do you set a clear color in OpenGL? I think I read something about it in a tutorial, something about an Alpha channel. 3.) Is there any way to optimize the height map tutorial so that it doesn''t use soooooo many verticies? I figured up that a 2048 X 2048 map uses 16,384 verticies! 4.) Does OpenGL have a built in water method? I think this is a rather dumb question. 5.) Does anyone know of a good physics tutorial for 3D? I found I need some help here, but I amazingly overcame the collision detection with an incredibly easy to implement method. Thanks guys, and I''ll probably be back here soon with some more questions. En taro Adun! Doom to all who threaten the homeworld! *Protoss Zealot - Starcraft*